Conducted by Professor Ian Hargreaves, Professor Justin Lewis and Tammy Speers, it looked at the relationship between British media coverage and public understanding of three issues: climate change, cloning and genetic research in medicine, and the controversy over the MMR vaccine. MMR is a three-part vaccine, given by injection, designed to immunise against measles, mumps and German measles (or rubella).

They analysed 2,214 newspaper, radio and television stories from January to September 2002, and compared this to data from two public opinion surveys of 1,000 people - one carried out in April and one in October the same year.

Controversy over the vaccine ignited in 1998 when British gastroenterologist Dr Andrew Wakefield suggested in The Lancet a link between the vaccine, autism and bowel disease in children. In early 2002, critics - including Wakefiled - questioned the validity of studies used by the British government to back the vaccine's safety, but the government resisted calls from critics to supply an alternative to the three-in-one MMR jab. Public confidence in vaccination fell.

Hargreaves and colleagues found that journalists too often gave the views of critics equal standing with the views of mainstream medical scientists, who argued that there was no scientific evidence for Wakefield's claims. The team then found that 53% of people surveyed believed that, because both sides got roughly equal coverage - often done in the interests of 'balance' - there must be roughly two equal bodies of evidence.

When asked if the bulk of evidence favoured supporters of the vaccine, 23% of the public agreed. The study also found that there was an increase in the percentage of people who favoured three separate vaccines as an alternative to the triple-dose MMR.

The researchers concluded that media coverage "was unintentionally misleading in creating the impression that the evidence for the link was as substantial as the evidence against it."

"In brief, while Wakefield's claims are of legitimate public interest, our report does give credence to the view that research questioning the safety of something that is widely used should be approached with caution, both by scientists publishing that research and journalists covering it."

When asked "If a scientist makes claims that go against the great majority ... how do you think the media should approach these claims?", 48% of the public chose the option: "Wait until other scientists confirm the findings", while 34% chose the option: "Give prominent coverage because it is news".

Not black and white

Commenting on the report, media researcher Dr Susanna Hornig Priest of Texas A & M University, told ABC Science Online it was common for public misunderstandings of science to be blamed on the media, but suggested the issue was not as black and white as it might seem.

She agreed that journalists were often trained to provide balance as an ethical standard, but that this could be problematic in covering science because it could ignore, distort or misrepresent the existence of scientific consensus and give too much support to minority points of view.

"Nevertheless, we should applaud media's trying to represent all viewpoints, in science as in politics. Scientific consensus is not always right, and if the media always reported the majority view in science as 'correct', the public would be done a serious disservice," said Priest, who is also an Associate Editor of the journal Public Understanding of Science.

Priest said the media should always report the existence of disagreement over scientific issues, but should not imply that all views are equally accepted by scientists and should make clear who is saying what.

She also said it was important not to overestimate the ability of the media to affect public opinion. She said studies into the effect of the media show that the press only tell people what things to think about (known as 'agenda setting'), and don't necessarily have a strong influence on exactly what their views are going to be (or 'opinion formation').

"If the media reported everything exactly right - whatever that would mean - people would not necessarily have their views changed," she told ABC Science Online.

Interestingly, Hargreaves' team found that the MMR story engaged the public much more than stories on climate change and medical genetics research. They said this was likely because it followed a familiar story line - in this case it was a maverick researcher and concerned parents questioning scientific officialdom.

The refusal of Britain's Prime Minister, Tony Blair, to declare whether his own son had been injected with the vaccine, made official government endorsements of the vaccine ring hollow, and exacerbated the problem, they said.

"The story's script was undoubtedly influenced by the ghost of the BSE controversy. Was this another case, reporters' asked, of mainstream science and the government rushing prematurely to the defence of the status quo?"